1PLY:
reference: Sodium ions and water molecules in the structure of poly(dA).poly(dT)., Chandrasekaran R, Radha A, Park HS, Acta Crystallogr D Biol Crystallogr. 1995 Nov 1;51(Pt 6):1025-35. PMID: 15299771

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).